1. Field of the Invention
The present invention relates to an ink composition used for ink jet recording, and a method for ink jet recording using the ink composition.
2. Description of the Related Art
Examples of an image recording method for forming an image on a recording medium such as a paper based on an image data signal include an electrophotographic method, a sublimation thermal transfer method, a melting thermal transfer method, and an ink jet method. The electrophotographic method requires a process of forming an electrostatic latent image on a photoreceptor drum by charging and light exposure, which makes the system complicated, and as a result, there is the problem such that production costs are high. In the thermal transfer system, although an apparatus is inexpensive, because an ink ribbon is used, there are problems such as high running costs and the generation of waste materials.
On the other hand, in the ink jet method, not only is an apparatus inexpensive, but in the ink jet method, since an image is formed directly on a recording medium by ejecting an ink only onto an area necessary for an image, ink can be used efficiently, and running costs are low. Additionally, the inkjet system generates less noise, and is therefore excellent as an image recording system.
As an ink composition cured by irradiation with actinic radiation such as ultraviolet rays (a radiation-curable ink composition) and usable as an ink composition for ink jet recording, an ink composition that is cured with high sensitivity and that can form high quality images is required.
When high sensitivity is achieved in a radiation-curable ink, high curability with respect to the irradiation with actinic radiation is also obtained. This provides various advantages, such as inhibition of volatilization of uncured low molecular weight substances, inhibition of a decrease in strength of an image formed, and the like, in addition to the advantages of an increased life span of equipment due to lower power consumption, a lower burden on an actinic radiation generator, and the like. Furthermore, the improvement in strength of a cured coating film due to high sensitivity of a radiation-curable ink composition provides high strength and durability to an image area formed by the ink composition.
An ink composition in which a combination of monomers having different functional groups selected from monofunctional monomers or polyfunctional monomers is used, has been proposed as an ultraviolet-curable ink composition (for example, see Japanese Patent Application Laid-Open (JP-A) No. 5-214280). Furthermore, a composition containing a polyfunctional acrylate has been proposed as a radiation-curable composition (for example, see JP-A No. 8-41133). These ink compositions have an excellent curing rate and enable the formation of a image free from bleeding. However, in these ink composition, since a polyfunctional acrylate is used as a main component of a curable composition, the flexibility of the cured product deteriorates, and due to volume contraction at the time of curing, adhesiveness (adhesion) to a recording medium also deteriorates.
Regarding adhesiveness of an ultraviolet-curable ink composition to a recording medium, a radiation-curable ink jet ink composition in which N-vinyllactam is used as a component for accelerating adhesiveness to a recording medium and flexibility of the cured product has been disclosed (for example, see JP-A No. 2004-514014). However, when N-vinyllactam represented by N-vinylcaprolactam is used, tackiness and leaching after curing may occur due to low copolymerizability with widely used radical-polymerizable monomers such as an acrylate, and additionally, the storage stability of an ink may deteriorate due to N-vinyllactam.
Thus, an ink composition usable in an ink jet apparatus and having excellent adhesiveness to a recording medium, excellent curing sensitivity, and excellent ejection stability, while maintaining image strength is desired; however, such an ink composition has not conventionally been available.